A PC (Personal Computer) becomes configured so that a main battery is of the built-in type. Therefore, the user cannot intentionally replace the battery. In order to enable a PC to be used for a long period of time, consequently, it is important to extend the life of a battery which decreases in characteristic over time.
For example, a Li-ion battery has characteristics in which the cycle characteristic is improved by lowering the charge voltage. However, if the current/voltage of charging a battery is constant, the cycle characteristic can not be improved.